JP2006086492A - Method to form surface equivalent to semiconductor substrate in terms of specific crystallography - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method to form a 45-degree surface of a semiconductor substrate having excellent surface smoothness to be used as a reflecting surface for optical source. <P>SOLUTION: The method to form a crystallographically equivalent surface to the ä110} surface or ä100} surface of a semiconductor substrate include the following steps. First, a semiconductor substrate having a top surface crystallographically equivalent to the ä110} surface or ä100} surface is prepared. Then, an etching mask with an etching window is formed on the surface crystallographically equivalent to the ä110} surface or ä100} surface. The etching window has a sidewall having a certain degree of a tilt angle with a direction crystallographically equivalent to the <100> direction or <110> direction of the semiconductor substrate. The tilt angle is greater than 0 degree and smaller than 90 degrees, and not equal to 45 degrees. After that, selective anisotropic etching treatment is performed using the etching window, thereby forming the equivalent surface to the ä110} surface or ä100} surface on the semiconductor substrate. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for forming a plane with a specific orientation, and more particularly to a method for forming a crystallographically equivalent plane with a {110} plane or a {100} plane of a semiconductor substrate.

  Referring to FIGS. 1A and 1B, a package structure of a single laser module used for an optical pickup is schematically shown. This laser module has a configuration in which a laser diode 102 and two light receivers 103 are arranged on a substrate 100. Laser light 104 emitted from the laser diode 102 is sent to a disk to be read through a lens (not shown) disposed above the laser module. Thereafter, the light reflected by the disc is received by the light receiver 103 and further processed in a subsequent procedure. Since the lens is not positioned in the path of the laser beam, conventionally, a microprism for guiding the laser beam upward is attached to the path of the laser beam. Alternatively, as a more advantageous method, as shown in FIGS. 1 (a) and 1 (b), the 45-degree surface 101 of the substrate 100 is used to achieve the same object without the need for a microprism. ing. As shown in the figure, the laser beam 104 emitted from the laser diode 102 is incident on the surface 101, is reflected by the surface 101, and passes through the lens. According to this method, the microprism is not required, and the manufacturing cost of the laser module can be reduced and the manufacturing process can be simplified.

  In order to properly reflect the laser light back toward the lens, the surface 101 must be an accurate 45 degree reflective surface. Please refer to FIG. 2A to FIG. 2C showing a process for forming the 45-degree surface 101 on the substrate 100. FIG. 2A is a schematic side view of a cylindrical crystal rod 200 whose upper surface is a crystallographically equivalent surface to the {100} plane. The cylindrical crystal rod 200 is cut along a broken line parallel to the upper surface, which is a crystallographically equivalent surface to the {100} surface, and a surface that is crystallographically equivalent to the {100} surface and < A plurality of silicon wafers 201 each having an orientation crystallographically equivalent to the 100> direction are obtained. Thereafter, as shown in FIG. 2B, an etching mask 290 (partially shown) having at least one etching window 299 is formed on a surface that is crystallographically equivalent to the {100} plane of the silicon wafer 201. The The side wall 298 of the etching window 299 is oriented at an inclination angle of 45 degrees with respect to a crystallographically equivalent direction to the <100> direction of the silicon wafer 201. Next, an anisotropic etching process is performed using a KOH-isopropanol etching solution in a state where the etching mask 290 is provided, so that a 45-degree plane 101, that is, {110, as shown in the sectional view of FIG. } A plane crystallographically equivalent to the plane is formed in the etching window portion of the silicon wafer 201.

  In practice, however, it has been found that the average surface roughness of the resulting surface 101 is not as low as desired and is typically on the order of 200 nm. The reason why the surface 101 is not smooth is that there are many microscopic surfaces crystallographically equivalent to the {111} plane as well as surfaces that are crystallographically equivalent to the {110} plane, and this is related to Sensors Actuators A. Vol. 48, pages 229-238 (1995), discussed in “Silicon anisotropic etching in KOH-isopropanol etchant” by Irena Barrycka and Irena Zubel. The reason is that the plane that is crystallographically equivalent to the {111} plane is more stable than the plane that is crystallographically equivalent to the {110} plane, and is therefore more likely to be induced during the etching process.

  The wavelength of the light source used in optical communication is usually in the range from visible to infrared, and the laser wavelength used in optical storage devices is also quite limited, so the surface roughness of the reflective surface is excellent imaging characteristics It is important to secure For example, the average surface roughness needs to be less than one-tenth of the wavelength of the incident light, otherwise significant dispersion loss of the incident light can occur. On the other hand, as the storage density increases, the operating wavelength of the light source of the optical storage device is limited. Therefore, an average surface roughness of 200 nm is not suitable for such applications, and therefore surface quality needs to be improved. As described above, a plane that is crystallographically equivalent to the {111} plane is more stable than a plane that is crystallographically equivalent to the {110} plane. That is, the inclination angle between the side wall 298 of the etching window 299 and the <100> direction of the silicon wafer 201 and the crystallographically equivalent direction is set to 54.74 degrees, and the difference of the silicon wafer 201 shown in FIG. When the isotropic etching process is performed, as shown in FIG. 2D, a surface 199 crystallographically equivalent to the 54.74 degree {111} plane having sufficient smoothness is formed. Therefore, another prior art utilizes a stable and smooth {111} plane and a crystallographic equivalent plane to obtain a desired 45 degree {111} plane and a crystallographic equivalent plane. This will be explained below.

  Please refer to FIG. 3 (a) to FIG. 3 (c). A cylindrical crystal rod 300 having an upper surface crystallographically equivalent to the {100} plane is cut along a broken line surface inclined by 9.74 degrees with respect to the upper surface to form a silicon wafer 301. Thereafter, as shown in FIG. 3B, an etching mask 390 (partially shown) having at least one etching window 399 is formed on the surface of the silicon wafer 301. The sidewall 398 of the etching window 399 is oriented at approximately 0 degrees with respect to a crystallographically equivalent direction to the <100> direction of the silicon wafer 301. Next, as shown in FIG. 3C, by performing an anisotropic etching process using a KOH-isopropanol etching solution, a surface 401 crystallographically equivalent to the 45-degree {110} plane is silicon. Formed on wafer 301. The average surface smoothness of the 45-degree surface 401 formed in this way is sufficiently improved. However, application of this process is limited. Since this silicon wafer is obtained by specially cutting the crystal rod at an inclined angle, the silicon wafer needs to be specially ordered. Further, as shown in FIG. 3 (c), in addition to the 45 degree plane 401, a plane 380 of 64.4 degrees on the opposite side of the plane 401 due to the specific crystallographic equivalent orientation of the silicon wafer 301 itself. Is formed.

  The present invention provides a method for forming a 45 degree surface of a semiconductor substrate having excellent surface smoothness used as a reflective surface of a light source.

  The present invention also provides a method for simultaneously forming opposing 45 degree faces in each etching window.

  According to a first aspect of the present invention, a method is provided for forming a crystallographically equivalent plane to the {110} plane of a semiconductor substrate. First, a semiconductor substrate having a plane that is crystallographically equivalent to the {100} plane is prepared. Next, an etching mask having an etching window is formed on a plane that is crystallographically equivalent to the {100} plane. The etching window has side walls oriented at an inclination angle with respect to a crystallographically equivalent direction to the <100> direction of the semiconductor substrate. The tilt angle is an angle greater than 0 degree, less than 90 degrees, and not equal to 45 degrees. Thereafter, selective anisotropic etching is performed using the etching window to form a crystallographically equivalent surface to the {110} plane on the semiconductor substrate.

  The semiconductor substrate preferably has a diamond structure crystal structure.

  The semiconductor substrate is preferably a silicon substrate.

  In one embodiment, the selective anisotropic etching process is a wet etching process performed with an etchant.

  In one embodiment, the etchant is a mixture of potassium hydroxide, water and isopropanol.

  In one embodiment, the selective anisotropic etching process is performed while stirring at a temperature of 60 to 95 degrees.

  The tilt angle is preferably 22 degrees or more and less than 45 degrees.

  The inclination angle is preferably greater than 45 degrees and 68 degrees or less.

  According to a second aspect of the present invention, a method is provided for forming a crystallographically equivalent plane to the {100} plane of a semiconductor substrate. First, a semiconductor substrate having a plane that is crystallographically equivalent to the {110} plane is prepared. Next, an etching mask having an etching window is formed on a plane that is crystallographically equivalent to the {110} plane. The etching window has sidewalls oriented at an inclination angle with respect to a crystallographically equivalent direction to the <110> direction of the semiconductor substrate. The tilt angle is an angle greater than 0 degree, less than 90 degrees, and not equal to 45 degrees. Thereafter, selective anisotropic etching is performed using the etching window to form a crystallographically equivalent surface to the {100} plane on the semiconductor substrate.

  According to a third aspect of the present invention, a method for forming a reflective surface of a semiconductor light emitting device is provided. First, a semiconductor substrate having a first specific crystal plane is prepared. Next, an etching mask having an etching window is formed on the first specific crystal plane. The etching window has side walls oriented at an inclination angle with respect to the crystal orientation corresponding to the first specific crystal plane. The tilt angle is an angle greater than 0 degree, less than 90 degrees, and not equal to 45 degrees. Thereafter, a selective anisotropic etching process is performed on the semiconductor substrate using the etching window to form a reflective surface known as a second specific crystal plane. The first and second specific crystal planes form an acute angle of about 45 degrees.

  In one embodiment, the first and second specific crystal faces are crystallographically equivalent faces to the {100} face and {110} face of the diamond structure.

  The foregoing description of the present invention will become more readily apparent to those of ordinary skill in the art upon reviewing the following detailed description and the accompanying drawings.

  In order to form one or a plurality of stable and smooth 45-degree surfaces on a semiconductor substrate by etching, according to the present invention, the inclination angle of the etching window formed on the semiconductor substrate with respect to the crystal orientation of the semiconductor substrate is selected. Hereinafter, an example will be described.

  Referring to FIG. 4A, a semiconductor substrate 500 made of silicon having a diamond structure crystal structure is shown. The semiconductor substrate 500 has an upper surface crystallographically equivalent to the {100} plane and an orientation crystallographically equivalent to the <100> direction, and a crystal rod (not shown) is the {100} plane of the crystal rod. Obtained by cutting along a plane parallel to the top surface which is crystallographically equivalent. An etching mask 530 having one etching window 540 is formed on a surface that is crystallographically equivalent to the {100} plane of the semiconductor substrate 500. The etching window 540 is obtained by forming a pattern and etching the etching mask 530 by a dry etching process. The side wall 541 of the etching window 540 is oriented at an inclination angle α with respect to a crystallographically equivalent direction to the <100> direction of the semiconductor substrate 500.

  As described above, if there are many microscopic surfaces crystallographically equivalent to the {111} plane as well as surfaces that are crystallographically equivalent to the {110} plane, the surface smoothness of the reflecting surface is lowered. A tilt angle of degrees is not suitable for forming an accurate 45 degree surface. On the other hand, according to a study by the inventors of the present invention, when the inclination angle α is greater than 0 degree and less than 45 degrees, or greater than 45 degrees and less than 90 degrees, a smooth 45 degree surface is obtained. .

  In the embodiment shown in FIG. 4A, the inclination angle α is selected to be larger than 0 degree and smaller than 45 degrees, for example, 22 degrees. After the etching window 540 having an inclination angle of 22 degrees is formed on the etching mask 530, a selective anisotropic etching process is performed with an etching solution having a temperature of 60 to 95 degrees. As a result, as shown in FIGS. 4 (b) and 4 (c), which are DD ′ and EE ′ sectional views of FIG. It is formed in the etching window portion of the substrate 500. An etching solution used for the selective anisotropic etching treatment is a mixed solution of potassium hydroxide, water, and isopropanol. The ratio of each component in the liquid mixture depends on the desired etching rate. During the selective anisotropic etching process, it is necessary to continuously stir the etching solution in order to remove bubbles that easily adhere to the 45 ° reflection surface and adversely affect the surface smoothness.

  With reference to FIG. 5A, another embodiment for forming a crystallographically equivalent plane to the {110} plane of the semiconductor substrate will be described. In the present embodiment, a step of forming the semiconductor substrate 500 and a step of performing a selective anisotropic etching process are included. These steps are the same as those shown in FIG. Will not be described. In this embodiment, the etching window 542 of the etching mask 530 has an inclination angle α between the <100> direction of the silicon wafer and a crystallographically equivalent direction and the side wall 543 greater than 45 degrees and smaller than 90 degrees, for example, It is formed to be 68 degrees. When the selective anisotropic etching process is performed, as shown in FIG. 5B and FIG. 5C, which are the FF ′ sectional view and the GG ′ sectional view of FIG. 5A, respectively. In addition, four-sided 45 degree surfaces 552 are formed in the etching window portion of the semiconductor substrate 500.

  Referring to FIG. 6A, a plurality of etching windows 548 and 549 are formed in the etching mask 530 on the semiconductor substrate 500. When the selective anisotropic etching process is performed, as shown in FIG. 6B, which is a cross-sectional view taken along the line HH ′ of FIG. It is formed in the etching window portion of the substrate 500. According to such a method, the complexity of processing the reflecting surface of the laser module is greatly reduced and the cost is greatly reduced.

In each of the above-described embodiments, the etching mask 530 used in the present invention is made of silicon dioxide (SiO ₂ ) or silicon nitride (Si ₃ N ₄ ), and after these are subjected to selective anisotropic etching treatment, It can be removed using hydrofluoric acid. According to the present invention, the acute angle formed by the {100} plane and the crystallographically equivalent plane and the {110} plane and the crystallographically equivalent plane is approximately 45 degrees with slight deviation. The inclination angle α is adjusted. According to the study of the inventors of the present invention, the average surface smoothness of the resulting 45 degree plane increases as the tilt angle α deviates from 45 degrees. On the other hand, the closer the inclination angle α is to 45 degrees, the smaller the angle deviation from the accurate 45-degree surface. This choice is left to the manufacturer and is determined by actual requirements. For example, when it is required to obtain a plane that is crystallographically equivalent to the {110} plane of 45 degrees, where the allowable deviation is ± 1 degree, the inclination angle α is in the range of 22-45 degrees or 45-68 degrees. Need to be adjusted.

  So far, the present invention has been described by referring to a method for forming a crystallographically equivalent plane to the {110} plane of a semiconductor substrate, but the present invention is not limited to other crystallographically equivalent planes. It can also be applied to other methods for forming. For example, according to the present invention, using a semiconductor substrate having a top surface that is crystallographically equivalent to the {110} plane and a crystallographically equivalent orientation to the <110> direction, Equivalent planes can be formed. As shown in FIG. 7 (a) and FIG. 7 (b), a tilt degree range α that is greater than 0 degree, less than 90 degrees, and not equal to 45 degrees is again applied to achieve the objective. The Furthermore, the present invention can be similarly used in a micro mechatronics system (MEMS) and optical communication.

  Although the present invention has been described above with respect to the most practical and preferred embodiments at present, the present invention is not limited to the disclosed embodiments, but is the broadest interpretation of the appended claims. It is intended to include various modifications and similar arrangements within the spirit and scope of the invention, and include all such modifications and similar structures.

(A) is a schematic perspective view of the package structure of the laser module used for an optical pick-up head, (b) is A-A 'sectional drawing of (a). (A) to (c) are schematic views showing a process of forming a crystallographically equivalent surface to a 45-degree {110} plane in a silicon wafer according to the prior art, and (d) is a silicon wafer according to the prior art. Schematic showing a sufficiently smooth 54.74 degree {111} plane and a crystallographic equivalent plane applied to the formation of a 45 degree {111} plane and a crystallographic equivalent plane. (A)-(c) is the schematic which showed another process of forming a crystallographically equivalent surface with the 45-degree {111} plane in the silicon wafer by a prior art. (A) is the perspective view seen from the upper side which shows roughly a part of silicon wafer in which the etching window was formed in order to perform an etching process by one Embodiment of this invention, (b) is D- of (a). It is D 'sectional drawing, and is a figure which shows roughly the surface which is crystallographically equivalent to 45 degree {110} plane which arises after the etching process, (c) is EE' sectional drawing of (a). The figure which shows roughly the crystallographically equivalent surface with the {110} surface of 45 degree | times produced after the etching process. (A) is the perspective view seen from the upper side which shows schematically a part of silicon wafer in which the etching window was formed in order to perform an etching process by another embodiment of this invention, (b) is F of (a). -F 'cross-sectional view schematically showing a plane that is crystallographically equivalent to the 45-degree {110} plane generated after the etching process, and (c) is a GG' cross-sectional view of (a). FIG. 4 is a diagram schematically showing a plane that is crystallographically equivalent to a 45-degree {110} plane that occurs after etching. (A) is the perspective view seen from the top which shows roughly a part of silicon wafer in which two etching windows were formed in order to perform etching processing by another embodiment of the present invention, and (b) (a) ) Is a cross-sectional view taken along the line HH 'of FIG. 4 and schematically shows a crystallographically equivalent plane to the 45-degree {110} plane generated after the etching process. (A) is a top view schematically illustrating a portion of a silicon wafer having an etching window formed to obtain a crystallographically equivalent surface to a 45 degree {100} plane according to one embodiment of the present invention. A perspective view, (b) from above schematically shows a silicon wafer having an etching window formed to obtain a crystallographically equivalent surface to a 45 degree {100} plane according to another embodiment of the present invention. FIG.

Explanation of symbols

500 Semiconductor substrate
530 Etching mask 540 Etching window 541 Side wall 550 45 degree surface

Claims (10)

A method of forming a crystallographically equivalent plane with a {110} plane of a semiconductor substrate,
Providing a semiconductor substrate having a crystallographically equivalent plane to the {100} plane;
An etching window having sidewalls oriented at an inclination angle greater than 0 degrees, less than 90 degrees and not equal to 45 degrees relative to a crystallographically equivalent direction of the <100> direction of the semiconductor substrate; Forming an etching mask on a plane crystallographically equivalent to the {100} plane;
Performing a selective anisotropic etching process using the etching window to form a crystallographically equivalent plane to the {110} plane on the semiconductor substrate.   The method according to claim 1, wherein the semiconductor substrate is a silicon substrate having a diamond structure.   The method according to claim 1, wherein the selective anisotropic etching process is a wet etching process performed while stirring with an etching solution having a temperature of 60 to 95 degrees.   The method according to claim 1, wherein the tilt angle is not less than 22 degrees and less than 45 degrees.   The method of claim 1, wherein the tilt angle is greater than 45 degrees and less than or equal to 68 degrees. A method of forming a crystallographically equivalent plane with a {100} plane of a semiconductor substrate,
Providing a semiconductor substrate having a crystallographically equivalent plane to the {110} plane;
An etching window having sidewalls oriented to form an inclination angle greater than 0 degrees, less than 90 degrees and not equal to 45 degrees relative to a crystallographically equivalent direction of the <110> direction of the semiconductor substrate; Forming an etching mask on a plane crystallographically equivalent to the {110} plane;
Performing a selective anisotropic etching process using the etching window to form a crystallographically equivalent plane to the {100} plane on the semiconductor substrate.   The method according to claim 6, wherein the inclination angle is 22 degrees or more and less than 45 degrees, or the inclination angle is greater than 45 degrees and 68 degrees or less. A method of forming a reflective surface of a semiconductor light emitting device,
Providing a semiconductor substrate having a first specific crystal plane;
An etching mask having an etching window having sidewalls oriented to form an inclination angle greater than 0 degrees, less than 90 degrees, and not equal to 45 degrees with respect to a crystal orientation corresponding to the first specific crystal plane; Forming on the first specific crystal plane;
Performing a selective anisotropic etching process on the semiconductor substrate using the etching window to form the reflective surface which is a second specific crystal plane, and
The first and second specific crystal planes have an acute angle of about 45 degrees.   9. The method according to claim 8, wherein the first and second specific crystal faces are crystallographically equivalent faces to the {100} face and {110} face of the diamond structure.   The method according to claim 8, wherein the inclination angle is 22 degrees or more and less than 45 degrees, or the inclination angle is greater than 45 degrees and 68 degrees or less.

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